Missing Thumbnails (3 posts)

I have recently built a new photography website http://www.anthonymayatt.co.uk and getting an issue where once you open a portfolio folder some thumbnails are missing. If you refresh the page different images may then have it missing with others loaded.

I have tried deactivating plug ins and putting them back 1 by 1 which does nothing and have also reduced the size of the files incase that was an issue.

Can anyone else please help as the site is ready to launch and do not want to while this issue is occuring.